Radioactive microspheres radioembolization offers promise for treatment of liver cancer. Radioactively labeled microspheres are injected directly into the blood vessel feeding tumor through hepatic catheterization. The injected microspheres can emit radiation for a very limited distance and surrounding normal tissues remain unaffected. For this purpose, variety of radioisotopes including rhenium-188 (188Re) has been used for labeling appropriate particles. 188Re is a radionuclide with a physical half-life of 16.9 h and has several advantages compared to other beta-emitting radionuclides. It emits beta particles with a maximum energy of 2.12 MeV and a 155 keV gamma ray, which are suitable for therapy and imaging. The HSA microspheres showed several advantages including biodegradable; bio-compatible; non-toxic and non-antigenic; uniform size; high mechanical stability to resist breakdown and passage through the capillary network and high chemical stability to resist radiolysis. Taken together, HSA microsphere is an ideal carrier for radionuclide.
Wang S. J. et al. described method for labeling resin microspheres with 188Re (Journal of Nuclear Medicine, 1998, 39(10): 1752-1757; Nuclear Medicine Communications, 1998, 19: 427-433). In this protocol, large amount of tin salt was used to radioactively labeling; however it may cause unexpected pharmacological effects. In addition, the acidify condition would hydrolyze proteins. Wunderlich et al. (Applied Radiation and Isotopes 2005, 62: 745-750; Applied Radiation and Isotopes 2005, 62: 915-918, Nuclear Medicine and Biology 2010, 37: 861-867; U.S. Patent: US20080219923 A1) disclosed 188Re labeled HSA microspheres. In this protocol, the radio-labeling process was carried out by combination of the reductive reaction of Re(VII) with Sn(II) and a particle surface-related co-precipitation effect of tin hydroxid colloid with reduced, hydrolyzed rhenium. The labeling yield is significantly higher and the amount of tin sale used in reaction is limited. However, in vitro stability is not stable. The particle-bound radioactivity was decreased to 86% within 48 hrs at ambient temperature. Hence, 188Re or tin chloride may release from microsphere surface and cause side effects.